The advantages of long-acting or sustained release products are well-known. Such products are of great value in the pharmaceutical field because medication can be administered for uniform and continuous release over a prolonged period of time to achieve a stable and desired blood level of the active ingredient without requiring frequent administration of the medicament. The sustained release composition must meet certain criteria, namely it must provide uniform and constant dissolution and efficacy for a prolonged period of time, it must be easy to prepare, it must have acceptable taste and must be adaptable for use with a variety of therapeutic agents.
The use of cellulosic materials such as hydroxypropyl methylcellulose as an ingredient in pharmaceutical formulations is known. For example, U.S. Pat. No. 3,590,117 describes the use of hydroxypropyl methylcellulose in long-lasting troches used as vehicles for administering active medicaments. U.S. Pat. No. 3,870,790, describes mixing an active therapeutic ingredient with a copolymer of premoisturized hydroxypropyl methylcellulose powder optionally mixed with ethylcellulose powder. The release period of the active medicament is a function of the moisture content of the cellulose carrier.
In U.S. Pat. No. 4,259,314 there is described compositions which employ hydroxypropyl methylcellulose of different viscosity grades and hydroxypropyl cellulose in a dry powder composition which has particular value for use with hygroscopic active ingredients.
U.S. Pat. No. 4,292,299 to Suzuki et al. describes a long-acting buccal preparation which includes an adhesive outer layer comprising polymers which have adhesiveness to a wet mucous surface and which swell upon moistening together with a nonadhesive layer which is water soluble or water disintegrable. At least one of the layers is made to contain the active ingredient. The polymers suggested for use in the adhesive layer include homopolymers of acrylic acid monomers such as polyacrylic acid and related salts.
None of the compositions described in the prior art have demonstrated completely satisfactory properties for the administration of large active ingredient molecules. In particular the prior art compositions have not satisfactorily solved the problem of administering such molecules via desorption from the composition in the buccal pouch of the mouth. Nor have the prior art compositions demonstrated completely satisfactory characteristics where it is desired to administer active ingredients over a 12 to 24 hour time period.